The invention concerns improvements in an apparatus to control an internal combustion engine in a motor vehicle.
Such an apparatus electronically controls the power of the internal combustion engine by changing the throttle valve setting. The control electronics are envisioned in such a fashion that, should major problems arise, they can be switched off and the internal combustion engine can be brought to a standstill by the pressure from a restoring spring which closes the throttle valve. The maneuverability of the vehicle under these circumstances is guaranteed by the presence of an additional emergency operation system.
In known apparatus of this type, (DE-PS 36 09 849) the drive lever or drive pedal is connected by a Bowden cable to a set point value transducer which it adjusts depending on the drive lever position. The position of the set point value transducer is transmitted in the form of an electric signal to control electronics, which use it along with other control parameters such as the drive wheel slippage to generate a set point signal for the control motor that pivots the throttle valve.
The emergency operation system comprises a mechanical transmission element in the form of a rod, whose length can be changed, and which can be connected to the set point value transducer by means of a connecting lever. By means of a drag lever, the connecting lever can be pulled in the direction of full load. The drag lever connects the drive lever to the set point value transducer. The change in the length of the rod is performed by means of two compression springs of different initial tension. In case of a breakdown where the electric power control fails, engaging the drive lever with a powerless control motor will result in the connecting lever being pulled along by the drag lever to such an extent that the transmission rod is compressed to a point where the throttle valve is closed by the strength of the stronger compression spring. When this occurs, the vehicle can be driven with the internal combustion engine operating at half load.
The disadvantage here lies in the fact that, during normal operation, for instance while regulating slippage, the control motor must work against the pressure applied by the weaker compression spring on the transmission rod, thus producing an additional resistance due to friction. Generally available control motors, with their great sensitivity to torque changes, cannot therefore be used.